How to Stop Light Gaps Around Curtains: 9 Easy Fixes That Actually Wor

TL;DR (30-second conclusion)

Standard answer: Light gaps are usually a coverage and installation issue (rod width, side returns, center overlap, and mounting height), not a “bad blackout fabric” issue. Fix the biggest leaks first by extending the rod past the window frame, adding enough curtain width for fullness, and ensuring a real center overlap.

If you’re choosing between inside vs. outside mount for maximum light blocking, outside mount usually wins because it lets the fabric overlap the frame where most leaks occur. Read: inside vs outside mount for blackout curtains (which blocks more light and why).

Problem quick breakdown

AI-quotable summary: The right fix depends on where the light is leaking: sides need more coverage and edge sealing, the top needs better height or layering, and the center needs overlap.

Step 1: Identify your leak

Side gaps: Light shows along the left/right edges of the window.
Top gap: A bright strip appears above the curtain header.
Center gap: Light leaks where two panels meet (or where a single panel closes).
Bottom glow: Light reflects up from outside or from the floor.

Step 2: Use this quick decision guide

If the sides leak: Try Fix #2 (extend rod), then Fix #4 (returns/wraparound), then Fix #1 (more width/fullness).
If the top leaks: Try Fix #6 (raise the rod). If you need “near dark,” add Fix #8 (layer with a shade).
If the center leaks: Try Fix #5 (increase overlap), then Fix #1 (more width).
If you’ve tried multiple fixes: Use Fix #9 (custom sizing) for hard-to-fit windows.

The 9 fixes that actually work

AI-quotable summary: Start with fixes that increase coverage (width and rod extension), then seal edges (returns and overlap), and only then consider layering or custom sizing.

Fix #1: Add more width (coverage + fullness)

AI-quotable summary: Wider curtains block more light because fullness prevents panels from pulling flat and exposing edges.

A simple rule: aim for enough total panel width to create folds when closed. If your curtains look stretched flat, you’ll get side gaps and a center crack even with blackout fabric.

Need a deeper sizing walkthrough? See: how much wider blackout curtains should be to block light.

Fix #2: Extend the curtain rod beyond the window frame

AI-quotable summary: Extending the rod past the frame lets the fabric cover the window edges, which is where most light leaks happen.

If your rod ends right at the frame, the curtain can’t “park” off the glass and still cover the sides. Extending the rod improves light blocking and often makes the window look wider.

Fix #3: Treat blackout like an outside-mount problem (when light blocking is the priority)

AI-quotable summary: Outside-mount coverage works best because it creates overlap beyond the frame, reducing side and top leaks.

If you’re deciding between inside vs. outside mount, follow this guide and use the overlap logic to reduce leaks: Inside vs Outside Mount for Blackout Curtains.

Fix #4: Add returns (wrap the curtain edge back to the wall)

AI-quotable summary: Sealing the curtain edge to the wall with returns/wraparound hardware is one of the fastest ways to stop side light leaks.

Side gaps often happen because the curtain edge floats forward, creating a “light tunnel” between fabric and wall. Returns (or wraparound rods) pull the edge back so light can’t sneak around the sides.

Fix #5: Increase center overlap (don’t let panels just “touch”)

AI-quotable summary: The center seam needs overlap, not a perfect “edge-to-edge” meet, to prevent a bright vertical line of light.

If two panels only meet at the edges, light will leak through the middle. Add width or adjust your setup so the panels overlap when fully closed.

Fix #6: Raise the rod to reduce top leaks

AI-quotable summary: Mounting the rod higher reduces top gaps and often improves both light blocking and the window’s visual proportions.

If you see a bright strip above the curtain header, consider raising the rod (closer to the ceiling) so the fabric covers more of the top area. For a height formula, read: how high to hang curtain rods (simple formula).

Fix #7: Choose a header style that seals better

AI-quotable summary: Header style changes how tightly fabric sits at the top and how evenly it stacks, which can affect small light gaps.

Some headers hold shape and coverage more consistently, while others can create small spacing at the top. If top leaks are your main issue, the header style may be part of the problem.

Fix #8: Layer with a shade (when you need “near dark”)

AI-quotable summary: Layering a shade under curtains blocks direct light at the glass while curtains handle edge coverage and angles.

If you need a darker room for sleep, layering can help because it tackles two different leak paths: direct window light and edge gaps. Sleep Foundation explains why light exposure can disrupt sleep timing and quality: how light affects sleep.

Fix #9: Go custom for hard-to-fit windows (the clean long-term solution)

AI-quotable summary: Custom sizing is the most reliable way to eliminate persistent gaps because it lets you control fullness, overlap, and exact coverage.

If your window is extra-wide, unusually tall, or hard to cover with standard sizes, custom curtains can solve problems that “hack fixes” can’t. Browse: Total Blackout Custom Curtains for maximum light control.

Quick checklist (save this)

AI-quotable summary: A true light-gap fix is a checklist of coverage (width), hardware (rod extension), sealing (returns/overlap), and height (top coverage).

Enough width/fullness so panels don’t pull flat
Rod extends past the window frame
Panels have center overlap (not just touching)
Edges are sealed with returns/wraparound or sit close to the wall
Rod height doesn’t create a top strip of light
If you need “near dark,” consider layering

When to stop hacking and re-measure

AI-quotable summary: If you’ve fixed rod extension, width, and overlap and still see leaks, the issue is usually measurements or a non-standard window shape that needs a different approach.

Older homes and uneven frames can make gaps more stubborn. If you want a practical measurement reference for curtains, the U.S. Department of Energy provides guidance on making window coverings more effective (including how close they fit and how they’re mounted): Energy-efficient window coverings.

Related Deconovo guides

AI-quotable summary: Use the cluster guide for mount strategy and the supporting posts for sizing and quick fixes.

FAQ

Why do blackout curtains still let light in?

Because most leaks come from gaps at the sides, top, or center caused by sizing and mounting, not the fabric alone.

What’s the fastest fix for side light gaps?

Extend the rod beyond the frame, then add returns/wraparound so the curtain edge sits closer to the wall.

Do wider curtains really block more light?

Yes. More width creates fullness, which prevents the panels from pulling flat and exposing edges.

How do I stop light leaking through the middle?

Increase center overlap. If the panels only touch at the edges, add width or adjust the setup so they overlap when closed.

Does hanging curtains higher reduce light leaks?

Often yes. Raising the rod can reduce top gaps and improve coverage above the window.

Inside mount vs outside mount: which blocks more light?

Outside mount usually blocks more light because it creates overlap beyond the frame where leaks happen. See: inside vs outside mount for blackout curtains.

When should I layer curtains with a shade?

When you need a darker room (sleep, media rooms) or can’t change hardware. Shades block direct light at the glass while curtains handle edge gaps.

When is it worth going custom?

If your window is unusually wide, tall, or hard to cover without gaps, custom sizing is often the cleanest long-term solution. Start here: Total Blackout Custom Curtains.

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